The present invention relates to the handling of a substrate in the manufacture of an integrated circuit. More particularly, the present invention relates to methods and apparatus for controllably discharging an electrical charge remaining on a substrate in a plasma processing chamber during wafer processing.
Substrates, such as semiconductor substrates or glass substrates, are typically processed using plasma processing chambers to perform various process steps during the manufacture of the resultant devices, e.g., integrated circuits or flat panel displays. These plasma-enhanced semiconductor processes are well known to those skilled in the art. An important aspect of this manufacturing process is the handling of the substrate during its overall processing. Typically the handling and transport of the substrate from one particular process to another is highly automated. As is known, one of the steps that is typically automated is the removing of the substrate from a plasma processing chamber after the processing of the substrate within the chamber.
FIG. 1 illustrates a typical plasma processing system 100 having a plasma processing chamber 102. Chamber 102 includes a base plate 104 and an electrostatic chuck 106 for supporting a substrate 108 during the processing of the substrate. A substrate lifting arrangement 109 includes an actuator 110 and a lifting mechanism 112 having three or more, e.g., four, lifting pins 114. As will be described in more detail below, the various components making up the lifting arrangement 109 are typically electrically conductive and lifting arrangement 109 is typically electrically connected to ground when there is no power to the chuck. Also, electrostatic chuck 106 includes a layer of dielectric material 116 for electrically insulating chuck 106 from substrate 108. Actuator 110 is arranged to move lifting mechanism 112 between a first position in which ling pins 114 do not engage substrate 108 and a second position in which lifting pins 114 engage and lift substrate 108 off chuck 106.
In order to remove the substrate from the plasma processing chamber, the substrate is typically lifted from the chuck using a substrate lifting arrangement such as substrate ling arrangement 109 described above. This allows a substrate transport mechanism (not shown) to grasp the substrate and transport the substrate to the next process step. However, in some cases, the substrate may tend to stick to the chuck. As is known in the art, this sticking problem is caused by an electrical charge which remains on the substrate after the processing of the substrate. If the substrate sticks to the chuck, the substrate may have a tendency to pop loose from the chuck as the lifting arrangement lifts the substrate. This popping off may cause the substrate to be displaced relative to its expected position for grasping by the transport mechanism If the substrate is not in its proper location, the transport mechanism may not be able to properly grasp the substrate and the overall system will have to be stopped so that the displaced substrate can be manually retrieved.
Various approaches have been used to avoid the substrate sticking problem. In a first approach, an additional step is added to the processing of the substrate within the plasma processing chamber. This additional step, referred to as plasma discharging, involves striking a plasma within the chamber which acts as a conductive path for the charge on the substrate to discharge to the wall of the chamber. However, this approach increases the processing time required to process the substrate within the chamber and reduces the throughput of the overall process thereby increasing the overall costs involved with using this approach. Also, this process is typically not able to filly discharge the substrate and therefore does not eliminate the potential for the sticking problem.
In a second approach, the lifting arrangement is electrically conductive and grounded as described above for FIG. 1. With this arrangement, when the lifting arrangement engages the substrate, any charge remaining on the substrate is discharged through the substrate lifting arrangement. Although this approach does not require any additional process steps and elates the sticking problem, in some cases, this approach may cause damage to portions of the substrate. This damage may be caused when relatively high voltage currents are concentrated into small areas of the substrate which are in direct contact with the grounded lifting pins. Although this damage may not occur for substrates having relatively thick oxide layers, as the oxide layers of the substrate get thinner and thinner in order to increase the density of components on the substrate and/or to improve device performance, damage due to these concentrated currents is more likely.
The present invention provides methods and apparatus for controlling the discharge of any electrical charge remaining on a substrate as the substrate is lifted by a lifting arrangement from a chuck. This avoids the sticking problem while also minimizing the chances of damaging the substrate due to high voltage currents concentrated through small areas of the substrate which are in direct contact with the lifting arrangement.